Problem: Evaluate $a+(-b)$ where $a = 4$ and $b = 2$.
Let's substitute ${a = 4}$ and ${b = 2}$ into the expression. $\begin{aligned} &\phantom{=} {a}+(-{b}) \\\\ &= {4}+\left(-{2}\right) \end{aligned}$ $= 4-2$ $=2$